Currently, 95% or more of the total supply of hydrogen peroxide is produced by an anthraquinone process. However, this anthraquinone process requires a procedure for regenerating an anthraquinone solution and a procedure for separating hydrogen peroxide from an anthraquinone solution and refining the separated hydrogen peroxide because many reaction steps are required to produce hydrogen peroxide and side products are formed in side reactions of the reaction steps [J. M. Campos-Martin, G. Blanco-Brieva, J. L. G. Fierro, Angew. Chem. Int. Ed., vol. 45, page 6962 (2006)]. Therefore, the production of hydrogen peroxide using an anthraquinone process has high energy consumption and high production costs, thus causing the price competitiveness of hydrogen peroxide to be decreased.
In order to solve the problems of an anthraquinone process, research into reactions for directly producing hydrogen peroxide from oxygen and hydrogen that do not produce side products other than water has been being made for a long period of time, but this research is not commercially available yet due to technical difficulties. This research is problematic as follows.
First, there is a problem with mixing oxygen and hydrogen. That is, a mixture of oxygen and hydrogen can very easily explode because it has a large explosive range depending on the mixing ratio of oxygen and hydrogen. When the concentration of hydrogen in air at a pressure of 1 atm is 4˜75 mol %, the mixture can be exploded by an ignition source. Here, when oxygen is used instead of air, the explodable concentration of hydrogen is enlarged to 4˜94 mol %. This explodable concentration of hydrogen is enlarged depending on the increase of pressure, thus increasing the explodability of the mixture [C. Samanta, V. R. Choudhary, Catal. Commun., vol. 8, page 73 (2007)]. Therefore, in the process of directly producing hydrogen peroxide using hydrogen and oxygen as reactants, the mixing ratio of hydrogen and oxygen is controlled within a safe range, and the concentration of hydrogen and oxygen is diluted with an inert gas such as nitrogen or carbon dioxide.
In addition to the above safety problem, there is another problem, which is that hydrogen peroxide, although produced, easily decomposes into water and oxygen because it is a very unstable compound, and it is not easy to acquire high hydrogen peroxide selectivity because a catalyst used to produce hydrogen peroxide is used to synthesize water. Therefore, in conducting research into reactions for directly producing hydrogen peroxide from oxygen and hydrogen, strong acids and halide additives together with high-activity catalysts have been researched in order to solve the above problems.
Reactions for directly producing hydrogen peroxide have been conducted using precious metal catalysts, such as gold, platinum, palladium and the like [P. Landon, P. J. Collier, A. J. Papworth, C. J. Kiely, G. J. Hutchings, Chem. Commun., page 2058 (2002); G. Li, J. Edwards, A. F. Carley, G. J. Hutchings, Catal. Commun., vol. 8, page 247 (2007); D. P. Dissanayake, J. H. Lunsford, J. Catal., vol. 206, page 173 (2002); D. P. Dissanayake, J. H. Lunsford, J. Catal., vol. 214, page 113 (2003); P. Landon, P. J. Collier, A. F. Carley, D. Chadwick, A. J. Papworth, A. Burrows, C. J. Kiely, G. J. Hutchings, Phys. Chem. Chem. Phys., vol. 5, page 1917 (2003); J. K. Edwards, B. E. Solsona, P. Landon, A. F. Carley, A. Herzing, C. J. Kiely, G. J. Hutchings, J. Catal., vol. 236, page 69 (2005); J. K. Edwards, A. Thomas, B. E. Solsona, P. Landon, A. F. Carley, G. J. Hutchings, Catal. Today, vol. 122, page 397 (2007); Q. Liu, J. C. Bauer, R. E. Schaak, J. H. Lunsford, Appl. Catal. A, vol. 339, page 130 (2008)]. Among the precious metal catalysts, the palladium catalyst is reported to exhibit relatively excellent activity, and this palladium catalyst is generally used in a state in which it is supported on a carrier, such as alumina, silica, carbon or the like.
Further, in order to improve the selectivity of hydrogen peroxide, acid is added to a solvent to prevent hydrogen peroxide from decomposing into water and oxygen, and halogen ions are added to a solvent or a catalyst to prevent oxygen and hydrogen from forming water [Y.-F. Han, J. H. Lunsford, Catal. Lett., vol. 99, page 13 (2005); Y.-F. Han, J. H. Lunsford, J. Catal., vol. 230, page 313 (2005); V. R. Choudhary, C. Samanta, J. Catal., vol. 238, page 28 (2006); V. R. Choudhary, P. Jana, J. Catal., vol. 246, page 434 (2007); C. Samanta, V. R. Choudhary, Catal. Commun., vol. 8, page 73 (2007); C. Samanta, V. R. Choudhary, Appl. Catal. A, vol. 326, page 28 (2007); V. R. Choudhary, C. Samanta, T. V. Choudhary, Catal. Commun., vol. 8, page 1310 (2007)]. Such additives, such as acid and halogen ions, serve to improve the selectivity of hydrogen peroxide, but cause the problems of corrosion, of elution of a metal, such as palladium or the like, supported on a carrier, thus decreasing catalytic activity; and, of requiring that hydrogen peroxide be separated and refined even after it is produced. Meanwhile, P. F. Escrig et al. reported that, when a palladium catalyst containing an ion exchange resin having a sulfonic acid group and a complex is used, high catalytic activity is exhibited even when only a very small amount of halogen ions is added without the addition of acid (U.S. Pat. Nos. 6,822,103 and 7,179,440).
Recently, various methods using nanotechnologies have been attempted in order to develop a high-activity catalyst which can be efficiently used to directly produce hydrogen peroxide from oxygen and hydrogen. For example, Q. Liu et al. developed a catalyst in which palladium nanoparticles are supported on active carbon (Q. Liu, J. C. Bauer, R. E. Schaak, J. H. Lunsford, Angew. Chem. Int. Ed., vol. 47, page 6221 (2008)), B. Zhou et al. insisted that nanoparticles phase-controlled by 110 plane exhibit excellent activity (U.S. Pat. Nos. 6,168,775 and 6,746,597), and J. K. Edwards reported that a catalyst in which a palladium-gold binary metal is supported on active carbon treated with nitric acid exhibits excellent hydrogen selectivity (J. K. Edwards, B. Solsona, D. Ntainjua, A. F. Carley, A. A. Herzing, C. J. Kiely, G. J. Hutchings, Science, vol. 323, page 1037 (2009)). However, in order to use the highly-dispersed nanoparticles as a catalyst, many technical difficulties, such as mass production, the prevention of metal elution, the prevention of sintering phenomenon in reaction, and the change in catalytic activity according to the phase transition of metal catalyst particles, must be overcome.
As described above, the method of directly producing hydrogen peroxide from oxygen and hydrogen has been researched for a long period of time due to its technical importance, but is still being researched academically and is limited to research into small-scale catalyst production and catalytic reaction. Therefore, in order to commercialize this method, it is keenly required to develop a catalyst which can be easily produced and which can exhibit remarkably excellent performance even under the reaction condition that additives, such as acids, halogen ions and the like, are used at a minimum.